Closed loop control analysis of variable frequency transformer (VFT)

Variable frequency transformer (VFT) is a controllable, bidirectional transmission device that can transfer power in-between power system networks. The first VFT was installed at the Hydro-Quebec´s Langlois substation, which interconnects the asynchronous power systems of Quebec (Canada) and New York (USA). Basically, it is a rotary transformer whose torque is externally adjusted in order to control the power transfer. The advantage of a VFT over that of a conventional PAR is that it can control power flow with more precision and controllability. In the paper, a closed loop digital simulation model of VFT and its control system are developed with MATLAB Simulink and a series of studies on power flow through the asynchronous power system networks are carried out with this model. Moreover, the various plots of power transfer under different conditions have been discussed.